High-pressure cylinders back in service after DOT, NIOSH approval
The Department of Transportation (DOT) has approved the redesign of Luxfer USA Limited’s 4,500 psi cylinders, which had been restricted to a working pressure of 4,000 psi since February 4, 1984, after a cylinder valve separated from its air tank during recharging. The accident was due to cracks that had developed at the neck area.
Luxfer’s 4,500 psi hoopwrapped aluminum cylinders (exemption number E72354500, which covers all cylinders produced from 1976 until February 1984) are being fitted with a chrome-plated steel ring that is heated and inserted at the neck to enable them to be safely filled to their maximum capacity of 30 minutes of air. According to Luxfer, the company has conducted extensive metallurgical studies and hydraulic and pneumatic burst tests; the cylinders did not burst at test pressures of 9,000 psi, twice the cylinders’ service rating.
Luxfer has begun a retrofit program to modify its existing 4,500 psi cylinders. The program, which consists of inspection, neck machining, installation of neck ring, as well as transportation will be funded by Luxfer if the work is completed before June 1, 1985. The company has set up retrofit centers in Placentia, CA; Edison, NJ; Indianapolis, IN; Dallas, TX; Chamblee, GA; and Mississauga, Ontario, to modify the cylinders.
The DOT and the National Institute of Occupational Safety and Health (NIOSH) has approved a 4,500 psi polar cylinder manufactured by Acurex. The extra air pressure in 4,500 psi cylinders may afford a firefighter the added time needed to complete a search or make a safe exit from a hazardous environment.
Under ideal conditions, NIOSH rates these cylinders at 30 minutes of air. However, under fire conditions, everyone uses a different amount of air, and the Occupational Safety and Health Administration (OSHA) requires that 25% of a cylinder’s capacity be used for exit time. According to a New York City Fire Department official, departmental tests conducted with 4,500 psi cylinders in a trapped situation yielded an average working time of 11 minutes and an exit time of 6-7 minutes. With 4,000 psi cylinders, the operating time was reduced to 8-9 minutes.
A fully overwrapped cylinder will prevent a catastrophic failure in the neck and base of the cylinder, according to the fire official, but, like any metal cylinder, it is susceptible to leakage.
In order to obtain DOT and NIOSH approval, air cylinders must pass a series of tests, including crushing, burning, filling and discharging 10,000 times, and overcharging. One out of every 200 cylinders undergoes this life-cycle testing, ending with deliberate destruction by being pressurized to four times its rated pressure.
Fully charged, the 4,500 psi cylinder weighs 14.4 pounds and has a 45-cubic foot capacity, according to Survivair, one of the self-contained breathing apparatus (SCBA) manufacturers that uses the Acurex cylinder. The cylinder has lightweight aluminum liners and is fully overwrapped with layers of glass filament. According to Acurex, a standard steel air cylinder of comparable capacity weighs approximately twice as much as the 10-pound 4,500 psi cylinder.
Acurex will deliver more than 12,000 of these 4,500 psi cylinders to Scott Aviation Inc., an SCBA manufacturer, by April of this year.